基于CISK理论对环境流场影响台风发生发展的分析

本文用一基于第二类条件性不稳定机制(CISK)的简单数值模式研究了由于非热成风的存在和环境风场垂直切变的水平变化对台风低压发生发展的影响。结果表明,环境风场的涡度分布在对流层低层为气旋性涡度随高度增加,而在对流层高层为反气旋性涡度随高度增加时有利于台风低压的发生发展;非热成风存在且与热成风符号相反时有利于台风低压的发生发展。      

不对称环流对台风强度变化的影响

利用卫星云图和NCEP再分析风场资料对0207号台风HALONG云系和风场变化特征进行了分析.结果表明,台风云系不对称的结构,台风西侧高空急流向台风中心的移动和辐散是台风迅速减弱的主要原因.为了了解不对称台风环流对台风强度的影响,还对比分析了0417号台风AERE、0216号台风SINLAKU在中国沿海减弱和重新加强的环流特征.在低层流入台风中心南侧的西风分量大,在高层流入台风中心西侧的北风分量小,有利于台风的加强.台风南、北两侧的东西向风场垂直切变梯度差异不利于台风加强.东西向风场垂直切变对台风强度的影响比南北向风场更重要.     

初夏南海台风的结构分析

根据对8005号南海台风的结构分析,初步得到以下几点:1)南海台风各物理量的水平分布不对称。其湿度中心和暧中心分别位于700hPa和300—200hPa。垂直运动在台风迅速发展时达到极值。2)台风范围内的对流层高层和低层分别存在东北风和西南风大值区,U分量的垂直切变零线在台风发展阶级呈东西向穿过台风中心附近,随着台风加强切变加大。3)通过与西太平洋台风的比较,认为对流层高低层散度之差和涡度之差与南海台风发生发展的关系密切。4)积云对流造成的潜热释放是台风发展期的主要热源。      

环境风垂直切变与登陆台风强度变化关系的统计分析

为了了解环境风垂直切变在登陆台风强度突变下所起的作用,利用1990-2004年登陆中国的111个台风的强度、登陆位置以及NCEP/NCAR每日4次等压面风场等资料,分析了风速垂直切变对台风登陆过程中强度变化的影响.结果表明,与海盆中相比,环境风垂直切变与登陆台风强度的线性相关性减小,滞后的时间长度减短;环境风垂直切变与滞后6～18 h的台风强度有不可忽视的相关性,与滞后6 h的台风强度相关最佳,相关系数为0.215;对于显著增强的登陆台风,其所处的环境风垂直切变不太大,平均在9 m·s-1以下,反之当环境风垂直切变在9 m·s-1以上时,登陆台风的强度也有可能显著减弱;与在华南登陆的台风相比,在华东登陆的台风其减弱型样本相对更多,其强度受风速垂直切变影响衰减得更快.     

强台风海鸥登陆期间近地层风特性分析

利用位于海南文昌市的90 m测风塔观测的强台风海鸥多层测风数据,分析了台风海鸥登陆期间近地层风场时空特征、湍流强度、垂直风切变及阵风因子等风场特性,分析结果表明:台风海鸥登陆期间,近地层各高度风速呈现"M"型双峰特征,最大风速出现在台风后风圈;台风过境前后,风向旋转了180°;近地层风速随高度升高而增大,各高度风速垂直切变符合对数和指数规律;粗糙度长度、风廓线幂指数、湍流强度、阵风系数等风场特性与风速呈负相关关系,随着风速的增加而降低;从台风外围至台风眼,粗糙度长度随风速呈现"增大-减小-增大"特征;台风眼内部风速垂直切变剧烈,前后风圈的风速垂直切变较弱;强风区湍流强度较弱,弱风区湍流强度较强;台风风圈的湍流强度随高度增加而减小,台风眼内湍流强度随高度先减小再增加;台风影响各阶段阵风系数随高度升高而减小,各高度层阵风系数遵循指数定律;阵风系数随风速的增大而减小,当风速达到一定强度时,阵风系数随风速变化不明显。     

台风“莫拉非”非对称环流与强度变化的关系

利用热带气旋定位资料和NCEP同化资料,通过动态合成方法分析0906号台风"莫拉非"的非对称环流特征,探讨非对称环流与"莫拉非"强度变化的联系。结果表明:"莫拉非"的环境风场水平切变以对流层低层经向风水平切变最显著,且超前于"莫拉非"的强度变化;热带气旋中心附近-6~6m.s-1的纬向风垂直切变密集带和北侧东风切变的南移,是"莫拉非"逐渐增强的有利条件;"莫拉非"中心附近存在高低层相对涡度垂直切变正值中心,其在热带气旋发展成台风时达到极大值。     

蒙古低涡影响下山东大范围雹暴的环境风垂直分布特征

本文从环境风场出发,着重分析了因蒙古低涡影响,造成山东大范围雹暴的6次天气过程。讨论降雹前12小时和降雹时环境风的垂直分布特征,云底到云顶间风速垂直切变,以及地面至14公里各层风的垂直切变。指出了有利于雹暴发生、发展的环境风垂直分布特征和风速垂直切变值范围。     

1604号台风“妮妲”近海加强垂直结构的诊断分析

1604号强台风"妮妲"(强台风级)于2016年8月2日03:35在广东省深圳市大鹏半岛登陆。采用中央气象台台风强度路径数据、NCEP/NCAR 1°×1°再分析资料,计算出台风"妮妲"中心附近的环境风垂直切变、相对涡度垂直切变、垂直速度、水汽通量等物理量,结果表明:1)台风"妮妲"具有明显的近海加强特征;"妮妲"中心附近存在呈纬向分布的垂直切变密集带,登陆前12~0 h密集带接近最密程度,"妮妲"中心垂直风切变平均值减小,台风强度增强,垂直风切变平均值增大,台风强度维持。2)"妮妲"中心附近相对涡度垂直切变增大,台风强度增强,相对涡度垂直切变减小,台风强度维持;"妮妲"中心附近垂直速度增大,台风强度维持或增强。3)"妮妲"中心上空的1 000~850 h Pa之间存在最大水汽通量净入流区。     

台风“苏拉”登陆福建后降水的非对称成因分析

利用常规天气资料、NCEP再分析资料、卫星云图、新一代天气雷达等资料,分析了2012年第9号台风"苏拉"降水预报失败的原因及其暴雨成因。结果表明:此次台风暴雨预报失败的主要原因在于预报过程中没有关注台风垂直结构的改变及其对降水落区的影响。"苏拉"台风暴雨是在中高纬稳定的环流形势下发生的,低层到高层引导气流的变化导致"苏拉"高层风暴中心向南倾斜;环境风垂直切变导致了台风降水的非对称分布,环境风垂直切变方向的左侧是强降水发展的区域;此外,随着台风环流中心在垂直方向发生偏移,改变了涡度平流的垂直分布,从而导致了福建省南部的暴雨。因此关注登陆台风中心在垂直方向的偏移对台风降水预报非常重要。     

热带低压台风的发生发展与其周围流场垂直切变的关系

本文从Charney所提出的第二类条件不稳定(CISK)理论出发,用动力学方法论证了:台风等热带低压系统的发生发展与其周围流场基本气流的垂直切变的水平分布是密切相关的。     

台风低压发展的数值模拟研究——凝结加热廓线的影响

本文用一个同时考虑Ekman抽吸和积云动量输送作用的二维轴对称原始方程模式,就对流凝结加热廓线对台风低压发展的影响进行了数值模拟研究。试验结果表明,对流层中下部有较强加热时,模式台风低压的低压环流发展较快;对流层上部有较强加热时,系统结构更类似于实际台风。在台风低压发展过程中,对流凝结加热廓线也会改变,最强加热可能由对流层中下部向中上层发展和传播,从而,台风低压发展既快、系统结构又类似于实际台风。这样一种过程可能正是热带低压发展为台风的一般过程。      

STUDY ON THE GENESIS OF ASYMMETRICAL DISTRIBUTION CHARACTERISTICS OF PRECIPITATION ASSOCIATED WITH THE TYPHOON HAITANG (2005) FROM THE VIEW OF ATMOSPHERIC FACTOR

The distribution of precipitation field from the typhoon Haitang (2005) during its landing on Fujian province shows obvious asymmetric feature. Based on the NCEP/NCAR FNL (Final Analysis) data, this study reveals the contributions of atmospheric factor to the asymmetrical distribution characteristics of precipitation associated with the typhoon, through the analysis of water vapor condition, vertical ascending motion condition, the calculation of the dry Q vector and its decomposition, and adiabatic heating in the air column of 1000hPa -600hPa (lower atmosphere) and 500hPa-100hPa (upper atmosphere). The results are as follows: (1) In the lower atmosphere, the humidity on both sides of typhoon path can be equivalent, while it is more wet on the right side than left in the upper atmosphere, which obviously presents asymmetric distribution characteristics. (2) Both range and intensity of the vertical motion on the right side are wider and stronger than counterparts on the left side no matter in the lower or upper atmosphere. (3) In the upper atmosphere, forcing role of atmosphere in vertical upward motion on the right side of typhoon path is the same as that on the left, while it is significantly different in the lower atmosphere, which is significantly broader in scope and stronger in the intensity, along with obvious asymmetric distribution characteristics. In addition, the further analysis of the Q vector decomposition indicates that the forcing effect of mesoscale weather systems on vertical upward motion is stronger than that of large scale weather systems in the lower atmosphere. (4) The adiabatic heating always exists on both lower and upper atmosphere, and the range and intensity of the adiabatic heating forcing showed asymmetric distribution on both lower and upper atmosphere. (5) In a summary, the upper atmosphere humidity conditions, the forcing role of lower atmosphere in vertical upward motion, especially, to mesoscale weather system, and adiabatic heating in the lower atmosphere, all show similar asymmetric distribution characteristics to that of precipitation field from the typhoon Haitang (2005), that is to say, the atmospheric factors as mentioned above are all contributed to genesis of the asymmetric distribution characteristics of precipitation.     

不同垂直加热率对爆发性气旋发展的影响

文章着眼于海洋温带气旋爆发性发展热力结构的影响效应问题。通过数值试验的结果表明，温带气旋发展状况对于垂直加热廓线分布具有突出的敏感性，若将垂直加热廓线“形变”，则可能导致海洋气旋的爆发性发展，并构成类似观测到的“气象炸弹”动力，热力结构，即“上干下湿”，“上冷下暖”的不稳定层结或“抽吸”结构，急流轴“断裂”形成的非地转偏差特征。从而揭示了垂直加热廓线特征在海洋气旋发展诸影响因子中的关键作用以及潜热释放分布与海洋气旋动力、热力结构形成的机理。     

爆发性发展台风附近次级环流的诊断分析

利用原始方程模式的Sawyer－Eliassen次级环流方程，对由5个爆发性发展的台风所合成的要素场进行了次级环流的诊断．结果表明，在各强迫项中，地转形变和非绝热加热强迫作用较大．大尺度加热主要加强中低层环沈，对流加热则主要加强中高层环流．台风爆发性发展前后，动力强迫和热力强迫的相对重要性不同．在台风爆发性发展时，非绝热加热强迫的相对重要性明显加大。     

台风内核与外围加热对其强度突变的影响

采用准动量无辐散模式，考虑非绝热加热过程，探讨了加热、惯性稳定度、层结稳定度以及非热成风等物理因子对台风中的重力惯性波强度变化的影响。进而把台风内核与外围的加热过程加以区别，指出要引起内核强度突变不仅要有非线性动力过程，而且要有非线性加热过程；而要引起外围强度突变则要有非线性动力过程以及定常的加热过程。     

A STUDY OF NUMERICAL MODELLING ON THE DEVELOPMENT OF DEPRESSIONS IN THE SOUTH CHINA SEA

The comparison analyses between two tropical depressions in the South China Sea are completed by numerical ex-periments with a limited area model developed in Guangzhou Institute of Tropical and Oceanic Meteorology. One of thedepressions develops and finally becomes a typhoon within 24 hours of the analyzing period (defined as DVD hereafter),and the other not (defined as UNDVD) The analyses show that their initial structures of temperature, humidity, pres-sure. wind and stability are obviously different from each other. There are a very deep wet layer and a clear warm-coredstructure in the mid-lower troposphere in the depression area in the DVD case, but with the warm core in the upperrather than lower troposphere arid a very shallow wet layer in the lower troposphere in the depression area in theUNDVD case. The developing and non-developing processes are successfully simulated by the model, showing that theCISK mechanism plays the most important role in the development of SCSDs (Tropical Depressions in the South ChinaSea). Several numerical experiments show that the structures of humidity and temperature in the depression area haveimportant effect on the development of SCSDs. It is favourable to the development of SCSDs when a very deep wet layerexists in the mid-lower troposphere or a warm-cored structure exists in the mid-lower troposphere instead of in uppertroposphere, and conversely, it is unfavourable to the development of SCSDs when the wet layer is very shallow in thelower troposphere or the warm-cored structure is in the upper troposphere rather than in mid-lower troposphere. Thestructures of stability for each case are also analysed, which shows evident differences between the two cases, with adeeper instability layer in the DVD case and a shallower one in the UNDVD case. Finally, the sensitivity of the devel-opment of the SCSDs to the vertical structures of humidity and temperature in the depression area is discussed.     

斜压涡度的变化与台风暴雨的关系研究

台风暴雨作为台风引起的最主要灾害之一,一直被人们关注。台风常被认为是对称结构,但从实际状况来看台风的非对称性非常明显,所以有必要研究斜压性涡度在台风中的表现。在高分辨率数值模拟的基础上,通过引入斜压涡度的概念,分析和总结了斜压涡度在2009年台风“莫拉克”暴雨过程中的表现。通过模拟与分析得到如下的结果:斜压涡度和MPV对比,可以看出在登陆前和登陆后,明显低层斜压涡度有更强的异常信号,围绕台风内核呈现正负正的位相特点;从沿着台风中心时间剖面可以看出,登陆前斜压涡度低层多为负正负的位相,并且随着时间的推移,斜压涡度有从大气的高层向台风的移动中心传递的趋势,即在台风即将到达时原先的正涡度被替换为负涡度,所以对其移动有一定指示意义;在台风“莫拉克”过台湾岛时,其斜压涡度表现为负涡度消失,在山地附近有正涡度生成,完成过岛,台风中心被替换;斜压涡度的异常值主要位于大气的低层时,一般会产生较强的降水。      

台风角动量平衡的诊断分析

本文根据文献[6],应用FGGEb资料,计算了7908号台风四个同心区域的质量收支和绝对角动量收支,得到以下结果:台风的演变过程可以由其旋转轴确定的绝对角动量来表征。在台风发展最盛时,对流层中层角动量达到最大;台风绝对角动量主要来源于水平侧边界输送。对于侧边界角动量输送,计算结果表明:在台风形成以前,涡动方式(非对称气流)输送是主要的;在台风形成初期,平均和涡动两种方式的输送具有同等重要性;在台风发展强盛及其减弱期,以平均输送为主。比较各强迫函数的作用,凝结潜热释放则是影响角动量垂直输送的重要因子。根据角动量平衡,发现次网格尺度效应显著,说明系统内部角动量再分配机制,除了角动量向上输送以外,积云对流活动可能是另一重要的方式。      

IMPACTS OF UPPER-LEVEL COLD VORTEX ON THE RAPID CHANGE OF INTENSITY AND MOTION OF TYPHOON MERANTI (2010)

Typhoon Meranti originated over the western North Pacific off the south tip of the Taiwan Island in 2010.It moved westward entering the South China Sea,then abruptly turned north into the Taiwan Strait,got intensified on its way northward,and eventually made landfall on Fujian province.In its evolution,there was a northwest-moving cold vortex in upper troposphere to the south of the Subtropical High over the western North Pacific(hereafter referred to as the Subtropical High).In this paper,the possible impacts of this cold vortex on Meranti in terms of its track and intensity variation is investigated using typhoon best track data from China Meteorological Administration,analyses data of 0.5×0.5 degree provided by the global forecasting system of National Centers for Environmental Prediction,GMS satellite imagery and Taiwan radar data.Results show as follows:(1)The upper-level cold vortex was revolving around the typhoon anticlockwise from its east to its north.In the early stage,due to the blocking of the cold vortex,the role of the Subtropical High to steer Meranti was weakened,which results in the looping of the west-moving typhoon.However,when Meranti was coupled with the cold vortex in meridional direction,the northerly wind changed to the southerly at the upper level of the typhoon;at the same time the Subtropical High protruded westward and its southbound steering flow gained strength,and eventually created an environment in which the southerly winds in both upper and lower troposphere suddenly steered Meranti to the north;(2)The change of airflow direction above the typhoon led to a weak vertical wind shear,which in return facilitated the development of Meranti.Meanwhile,to the east of typhoon Meranti,the overlapped southwesterly jets in upper and lower atmosphere accelerated its tangential wind and contributed to its cyclonic development;(3)The cold vortex not only supplied positive vorticity to the typhoon,but also transported cold advection to its outer bands.In conjunction with the warm and moist air masses at the lower levels,the cold vortex increased the vertical instability in the atmosphere,which was favorable for convection development within the typhoon circulation,and its warmer center was enhanced through latent heat release;(4)Vertical vorticity budget averaged over the typhoon area further shows that the intensification of a typhoon vorticity column mainly depends on horizontal advection of its high-level vorticity,low-level convergence,uneven wind field distribution and its convective activities.     

Betts对流调整方案在移动套网格台风数值模式中的初步试验

Betts对流调整方案采用的是垂直温湿场向观测的准平衡热力结构松驰的方法。本文在一个考虑了台风初值化的移动套网格台风数值模式中,对Betts方案进行了初步试验。结果表明：Betts方案能较好的预报出台风移动的路径和降水过程,并在台风路径、降水落区预报以及对流增温的垂直分布等方面都略优于Kuo方案的预报结果。